A 28-year-old man is suspected of killing a 6-month-old boy.
Grant Edwin Johnson was arrested Friday afternoon by the Yellowstone County Sheriff's Office on suspicion of deliberate homicide.
Yellowstone County Sheriff's deputies and Emergency Medical Services responded to reports of an unresponsive infant at a residence off South Frontage Road on the afternoon of May 27, said YCSO Lt. Kent O'Donnell.
The child was taken to St. Vincent Healthcare.
"Our coroner began investigating the death portion of it and then when things didn't look quite right, information we got was suspicious," O'Donnell said. "Then of course the medical opinion at the hospital also raised questions. Then detectives were called in and began their investigation into the circumstances surrounding the death."
"Detectives have been working on this all week," he said, adding they interviewed "multiple witnesses."
Johnson is expected to appear in court Monday, O'Donnell said.
O'Donnell declined to release more details about the circumstances of the child's death, but said those would be available when charging documents were made public.
No other arrests have been made as a result of the investigation, O'Donnell said.
The investigation is ongoing, said Sheriff Mike Linder.